1. Field of the Invention
The present invention relates to a shuttle type recording apparatus for recording characters and images on a recording medium while scanning a recording head against the recording medium. More particularly, the present invention relates to a serial type recording apparatus in which a plurality of recording head arranged at a predetermined interval can record divided recording areas for the respective recording heads.
The present invention is particularly suitable for a recording apparatus for recording by applying coloring agent on the recording medium in accordance with image data, and it is more particularly suitable for an ink jet type recording apparatus in which liquid recording ink is discharged as the coloring agent to make a record.
The present invention is applicable to any equipment which uses the recording medium such as paper, cloth, skin, unwoven cloth or OHP sheet and further metal or the like. Specific application equipments include office products such as a printer, a copying machine and a facsimile machine and industrial manufacturing machines.
2. Related Background Art
The serial type recording apparatus in which recording is made while scanning the recording head has been commonly used in various recording apparatus because it is less expensive than a recording apparatus in which recording is made by using a full line head which covers an entire width of the recording medium.
In the serial type recording apparatus, a material which reacts to a heat generation element of a thermal head to a dedicated thermal sheet and a material which cause a dedicated photo-sensitive sheet to optically generates a recording color have been known as the material to generate color of the coloring agent to the recording material. As a system to make a record by applying the coloring agent to the recording material by the recording head, various systems have been put into practice and proposed. For example, an impact recording system in which an ink ribbon having liquid ink impregnated as the coloring agent is pressed and abutted against the recording medium by a print wire to transfer the ink, a thermal fusion transfer recording system or a thermal sublimation system in which a heat generating element of a thermal head is reacted to an ink ribbon head having a solid coloring agent applied to transfer the ink and an ink jet system in which liquid recording ink is discharged to make a record.
Recently, from a stand point of plain sheet recording, the latter recording system for applying the coloring agent is main stream. Among them, the ink jet recording system has advantages of low noise, low running cost, easiness to make the apparatus compact, ability of plain sheet recording and easiness for color recording, and has been commonly used in the recording apparatus such as a printer and a copying machine.
In the serial type recording apparatus, recording heads each of which allows the recording only in a relatively small limited area of the recording element such as a discharge port provided in the recording head are arranged on a carriage and they are sequentially scanned to make a record. Thus, it is relatively difficult to increase a recording speed and the increase of the recording speed has been a problem for the serial type.
On the other hand, in order to increase the speed of the image recording, it has been proposed and put into practice to increase a recording width (arrangement range of recording elements) of the recording head, to increase the carriage speed and a recording frequency to reduce a scan time or to scan bilaterally to make a record. However, each system has limitation. For example, in order to increase the recording width, corresponding improvement of precision in manufacturing the head is required and the recording head becomes expensive and a capacity of print buffer for temporarily storing the record data increases so that a problem is raised in terms of cost. In the system in which the color is generated by utilizing heat or the coloring agent is applied, means for preventing the deterioration of the recording quality or the break of the head due to self-temperature-rise of the recording head is needed particularly when the recording width is large. In the ink jet recording system in which the liquid recording ink which is not in contact with the recording medium, when a recording head of a large recording width, means to prevent the deterioration of the recording quality due to cockling of the recording medium by absorption of moisture of the ink is complex. When the recording frequency is raised, it is necessary to increase the scan speed of the carriage to maintain a certain pixel density, but in this case, a load of a drive source increases and the recording quality may be deteriorated by vibration of the ink in the recording head due to the high speed of the carriage.
A system which is relatively effective to increase the speed of the serial type image recording apparatus is disclosed in JP-A-50-81437 and U.S. Pat. No. 4,272,771. This reference discloses that, in order to concurrently print on a left half and a right half of a print line, a left print head assembly and a right print head assembly supported by one carriage mechanism are used to attain the speed-up of approximately two times. It also teaches that a higher recording speed may be attained by increasing the number of print head assemblies to more than two or conducting the bilateral printing.
However, the prior art disclosed in the reference, in most cases, divides the recording areas merely from a stand point of high speed of recording. Accordingly, a construction which positively considers an overlapping recording area duplicatedly scanned by a plurality of heads is not disclosed. From a view point of high speed recording, it teaches that the overlapping recording area should be excluded as much as possible. Such overlapping recording area is not utilized as a recording area which is different from the recording area comprising divided recording areas.
As an application of the above, the recording in an area which is a combination of divided recording areas of several recording heads and the recording for a recording medium fed to various locations (positions) with various sizes may be used.
When such recording areas various sizes and positions are used, it is preferable that the apparatus is properly constructed. It is also preferable that the size of the recording apparatus does not increase in spite of the capability of recording on a recording medium of a relatively large size.
In order to attain the above, it is necessary to consider a reference position when recording sheets of various sizes are fed. Further, in order to make the apparatus compact while using the recording sheet of a large size, it is necessary to make the movement range of the carriage to be substantially equal to the recording area while securing the recording area by the divided recording areas corresponding to the large size.
Further, in such a case, it is preferable to consider the arrangement position of a maintenance unit for the recording head which does not directly relate to the recording. It is particularly preferable to consider the arrangement position in connection with the reference position of the recording sheet.
As the maintenance unit of the recording head, in the ink jet recording system, a mechanism for recovering the discharge to solve a problem due to the use of liquid ink has been known. For example, as means for cleaning out foreign materials such as droplets and paper powder deposited on the discharge port surface by the jump-back of ink mist or ink droplets from the recording medium, a construction to wipe the discharge port surface by a blade (wiper) formed by an elastic member such as rubber has been commonly adopted. Further, a cap is applied to the discharge port surface during non-record mode to prevent the evaporation of the ink in the recording head and the increase of viscosity and solidification of the ink. When the increase of viscosity or the solidification occurs and the discharge fails or the foreign materials on the discharge port surface cannot be removed by the blade, the high viscosity ink in the discharge port is ejected by a suction pump linked to the cap to recover normal discharge.
Further, in the recording operation of an on-demand type ink jet recording system, all of a plurality of discharge ports provided in one head are not always used and there are non-use discharge ports which are not used for certain time period. When a plurality of recording heads are provided such as in a color recording apparatus, all of the recording heads may not be used when record data is not transferred (no recording). If the carriage is scanned or stopped while the discharge port surface is not capped, the ink on the discharge port surface and in the discharge ports to which the inks are not continuously supplied for certain time are evaporated and dried, and the discharge performance and the record image quality are lowered. In the construction for making the records in various recording areas by using a plurality of recording heads as described above, there may be a head which does not discharge the ink depending on the recording area and it is preferable to consider the countermeasure to the failure of discharge caused thereby.
Together with the above recovery unit, it has been commonly conducted to discharge the ink at a predetermined position at a predetermined time interval without regard to the record data to eject the ink in the discharge port to keep the ink fresh so that the proper discharge condition is always kept. Such ink discharge operation is known as preliminary discharge. The discharged ink by the preliminary discharge is usually discharged toward the cap in the recovery unit or separately provided preliminary discharge receptacle to prevent the scatter to the recording medium and the inside of the recording apparatus.